Moisture profile

from Wikipedia, the free encyclopedia

As a moisture profile in which is remote sensing and meteorology measurement and analysis of the vertical profile of the humidity and the water vapor referred -content. It is mainly done via artificial earth satellites .

Satellite-based measurements

Since the 1980s, numerous earth observation satellites have been equipped with measuring instruments that determine the natural or reflected radiation of the earth's atmosphere in the frequency range of microwaves . These so-called microwave radiometers were first used (passively) around 1965 in the TIROS satellites in the USA, later in the Envisat and also actively (by emitting their own microwaves) in other environmental and weather satellites . For special purposes in geohydrology , the use of measuring aircraft is also possible.

The vertical gradients of the humidity can also be determined by measuring in two frequencies . For example, the passive microwave radiometers of the European satellites ERS-1 and ERS-2 work in the radio frequencies 23.8 and 36.5 GHz to measure the water vapor content of the troposphere.

The amount of atmospheric water vapor is important for meteorology (frontal course, weather forecast, etc.) on the one hand , and for geodesy and navigation for the precise reduction of radar distance measurements such as GPS and altimetry on the other . Water vapor and aqueous aerosols have a strong influence on the refractive index of waves in the radar range .

Water vapor in the atmosphere

The troposphere (lower 10-18 km of the atmosphere) contains between 0.5 and 4 percent by volume of water vapor , depending on the air temperature , climatic zone and weather conditions . Divided by the saturation vapor pressure (see dew point ) results in the relative humidity , an important parameter for meteorologists:

Water vapor is 37% lighter than dry air, which is why moist air is often pushed upwards and has a significant impact on the weather. In addition, moist air has a higher temperature gradient when ascending (because of the heat of condensation), so that vertical movements increase in intensity (e.g. in thunderclouds ). The level of condensation, in turn, is important for cloud formation and the precipitation forecast.

The water vapor content varies widely around its mean value of around 1.4 percent and is the most important “weather engine” alongside the air temperature . Above the condensation layers it is very low, so that only 0.4% results on average over the entire atmosphere. Above the tropopause , the air is almost dry.

Literature (basics)

  • Heinrich Faust : The structure of the earth's atmosphere , 308 pages, Vieweg-Verlag, Braunschweig 1968
  • Alois Sieber: Physical basics of remote sensing , 180 pages, research report DFVLR 86-37, Oberpfaffenhofen 1986